If you're only hosting websites, not email, then <a href="https://serverpilot.io/">ServerPilot</a> is probably the best zPanel alternative on DigitalOcean.
Since free panels sometimes decide to "commit suicide" (like zPanel did), now I never look to their side. It's better and ain´t no harder to find affordable solution which will work 4eva:)
You said that want to host a couple clients sites, so in case that you will need to set various PHP modes for different domains, users roles, access to different folders, etc I could recommend you ISPmanager hosting panel. It's really popular in Eastern Europe - and low cost isn't the only factor of popularity:)